Elaine de Kooning’s attempt to capture the essence of John F. Kennedy in the vivid colors and broad brush strokes of abstract art resulted in the striking portrait that is on permanent exhibit in the Hall of Presidents at the National Portrait Gallery. The story of how she came to paint it is even more extraordinary, and illustrates why capturing Kennedy on a canvas or in a book can be so challenging, and such an obsession, for artists, biographers and historians.

The trustees of the Truman Library chose de Kooning to paint the notoriously restless Kennedy because she had a reputation for being “the fastest brush in the East,” capable of finishing a portrait after a single sitting. When she arrived at the Kennedy family’s Palm Beach, Fla., estate on Dec. 31, 1962, she planned on making some quick sketches before finishing the portrait in a temporary studio in West Palm Beach. She stayed for four days, drawing dozens of sketches, charcoals and watercolors, and working on several oil portraits at once.

She returned to New York with her sketches and portraits, and soon there were more, many more. During 1963 she drew and painted only Kennedy, sketching him when he appeared on television and clipping photographs from newspapers and magazines that she used as models for more drawings and oils. She had, she admitted to a friend, fallen “a teeny little bit in love with him.” After running out of space in her studio, she papered her living quarters with more sketches and photographs, so that whenever she cooked, ate or took a bath, she saw him.

I can sympathize. Anyone visiting my office while I was completing “JFK’s Last Hundred Days” would have come across a similar scene. I had started with one bookshelf with 40 books — memoirs by members of Kennedy’s inner circle; biographies of JFK, Jackie, Teddy, Bobby and Rose. Within months I had five bookshelves and more than 300 books. I listened to his news conferences (he gave one every 16 days, on average); watched his home movies; bought the books he read during these last days, and read them; and photocopied the newspapers he read, and read those, too.

I did all this because I was gripped by the challenge of creating a definitive portrait of one of the most complicated, secretive, elusive and enigmatic men ever to occupy the White House, and of solving what I consider the greatest Kennedy mystery of all: not who killed him 50 years ago, but who he was when he died.

Even those who knew Kennedy well have spoken about the seeming impossibility of knowing him in his entirety. Ted Sorensen, his principal aide and speechwriter, believed that “different parts of his life, work, and thoughts were seen by many people — but no one saw it all.” Even Jackie threw up her hands, calling him “a simple man, yet so complex that he would frustrate anyone trying to understand him,” and concluding that “to reveal yourself is difficult and almost dangerous” for people like the Kennedys. “I’d say Jack didn’t want to reveal himself at all.”

For a Kennedy biographer, comments like these are like a red flag to a bull.

One of the greatest challenges Kennedy poses to anyone writing about him is that, because he rigorously compartmentalized his friends and family members, their impressions and recollections of him are sometimes at odds. He was intellectually closer to Sorensen than to any other adviser, yet the two men did not socialize, and the president never invited Sorensen to the intimate dinners at the White House family quarters (at which former Washington Post editor Ben Bradlee was a frequent guest). Bradlee says he knew nothing about Kennedy’s energetic philandering, yet Kennedy’s trusted secretary Evelyn Lincoln knew about his womanizing and in at least one instance offered her home address so he could receive letters from a mistress there.

Three days before going to Dallas, he told Lincoln he was thinking of replacing Lyndon Johnson with North Carolina Gov. Terry Sanford as his running mate in 1964, but he did not share this bombshell with his brother Bobby. Bobby later dismissed the conversation as a fabrication, telling historian Arthur Schlesinger, “Can you imagine the president ever having a talk with Evelyn about a subject like that?” Yet when former Cabinet member Abe Ribicoff went sailing with Bobby several months after Dallas, he was shocked to discover that he knew things about John that Bobby did not.

The recent release of revealing new material has made an understanding of the multifaceted Kennedy more attainable. Yet, even if there are no more great JFK revelations, biographers and historians will continue to be drawn to this elusive man because, as Kennedy once told his friend Bradlee, “What makes journalism so fascinating and biography so interesting ‘is the struggle to answer that single question: ‘What’s he like?'”

Thurston Clarke is the author of “JFK’s Last Hundred Days: The Transformation of a Man and the Emergence of a Great President.” He wrote this for the Washington Post.